The present invention relates to an instant film pack in which peel-apart type instant film units are contained and removably held.
Certain types of instant film units of the diffusion transfer type are generally contained in a film cassette or film pack in stacked relation and removably held therein. Especially a peel-apart type instant film unit (which is hereinafter referred to as a film unit for simplicity of description), as is disclosed in detail in Japanese Patent Publ. No. 44-2528 for example, basically comprises a photosensitive sheet for forming a latent image thereon and an image-receiving sheet adapted to be registered with the photosensitive sheet for processing in order to form a positive image of the latent image thereon. The film unit is designed to superpose the separate sheets relative to each other after exposure, for diffusion transfer processing. For this purpose, the photosensitive sheet is connected with a carrier sheet and, on the other hand, the image-receiving sheet has superposed thereon a mask sheet having an aperture by which an image-receiving area is defined thereon. The mask sheet is coupled to the carrier sheet.
Such film units are contained in stacked relation in a film pack which has a film unit exit slot at its front end and is used in cooperation with a camera back or a pack holder provided with a pair of pressure-applying members in the form of elongated rollers for applying compressive pressure to the superposed sheets so as to distribute processing liquid therebetween while the exposed sheets are withdrawn from the pack holder.
Upon withdrawing an exposed film unit, a tab relatively weakly connected to the carrier sheet at its leading end is at first withdrawn through a tab exit slot in the pack holder formed apart from the film unit exit slot so that the leading end of the carrier sheet emerges from the pack holder to allow access thereto for withdrawal. When the tab is further withdrawn, the tab is disconnected from the carrier sheet, and the leading end of the carrier sheet proceeds between the pressure-applying rollers. By withdrawing the leading end of the carrier sheet, the photosensitive sheet and the image-receiving sheet are drawn between the pressure-applying rollers and superposed in proper registry relative to each other.
Inside the pack holder there is a guide plate for directing the leading end of the carrier sheet withdrawn from the film pack toward and between the pressure-applying rollers. Between the front end of the guide plate and the pressure-applying rollers there is an edge controlling member disposed for compressively grasping the side edges of the superposed photosensitive and image-receiving sheets to positionally restrict the sheets and to prevent any escape of processing liquid distributed therebetween. This edge controlling member is suspended by a spring member for upward and downward displacement and guides the carrier sheet, and hence the film unit, toward the pressure-applying rollers in cooperative with the guide plate.
When assembling the pack holder, there is often a difference in level between the front edge of the guide plate and the edge controlling member due to manufacturing and/or assembling errors. Such a level difference will block the progress of the leading end of the carrier sheet. For avoiding this level difference, a fine adjustment of the spring force can be performed or an improved supporting mechanism can be provided for the edge controller. These countermeasures are, however, accompanied by great technical difficulties and are costly.
For the reasons stated above, there is thus a substantial chance that the leading end of the carrier sheet will not enter properly between the pressure-applying rollers; and this prevents the instant film unit from successfully emerging from the pack holder even though the tab is properly pulled out.